Sheryl Sandberg

After four years as Facebook's COO--and shepherding the company through its much anticipated and critiqued $100 billion IPO in May--Sandberg was named to the social network's board of directors in June. She is Facebook's first female board member and owns nearly $1 billion of unvested stock in the company. The Harvard MBA served as chief of staff for the U.S. Treasury Department under President Bill Clinton, and managed Google's online global sales and operations as a vice president. One of few prominent women in tech, Sandberg has become the torch-bearer for a generation of women hoping to balance high-profile jobs with motherhood, an increasingly fraught issue in 2012. "I don't believe in 'having it all,'" she says. "But I do believe in women and men having both a successful career and family. The more women we get into positions of power, the more likely we'll get that."